Network establishment and management protocol

ABSTRACT

The invention relates to a protocol for communications between networked devices. The devices are logically arranged as a hierarchy of device types including a controller device type ( 52 ) from which no other device type depends and a basic device type ( 54 ) from which a number of other device types depend. The devices implement a simple device description message of fixed length and format which includes the device type, and some devices further implement an extended device description message including additional information.

This invention relates to a network protocol, and in particular toimplementations of the protocol.

A prior art protocol for network management is universal plug and play(UPnP), which is very useful for internet applications where bandwidth,battery consumption, and to an extent cost, are not an issue.Implementations of the protocol in consumer electronics (CE) do exist,but because of the extent of the protocol, such implementations impose aheavy load especially on the simplest devices that otherwise wouldrequire only minimal processing capability.

The need therefore exists for a protocol suitable for embedding insimple devices such as lights, thermostats and CE equipment (remotecontrol for TV's, DVD's and PVR's), that is simple and cost effective toimplement, requires the minimum of bandwidth, yet is scalable across arange of devices with varying capabilities.

This need is not restricted to wireless application, but extends towired applications.

According to a first aspect of the invention there is provided a system,comprising: a plurality of networked devices each having a transceiverfor sending and receiving network messages; at least one networkeddevice arranged to send a simple device query message to other devicesand to receive and interpret simple device description messagessubsequently received from the other devices; at least one networkeddevice arranged to send an extended device query message to otherdevices and to receive and interpret extended device descriptionmessages subsequently received from the other devices; each of thenetworked devices being arranged to respond to an incoming simple devicequery message from another of the devices by sending a simple devicedescription message of defined length including a device type valuerepresenting the type of the device; and at least one of the networkeddevices is arranged to respond to an incoming extended device querymessage from another of the devices by sending an extended devicedescription message.

Such a system implements the protocol that is the subject of this patentapplication. The protocol itself will be referred to as home uniformcontrol language (HUCL).

In comparison, those prior art systems of which the inventors are awareimplement only a single device description message and response. Byproviding a simple device description of defined length and an extendeddevice description of variable length the invention makes it possible tocombine using the HUCL protocol simple devices operating only using thesimple messages and complex devices which make use of the greaterfunctionality available from the extended device description of variablelength. Simple devices may simply ignore extended device descriptionqueries.

The Simple Device Description includes a small or moderate number ofpredetermined fields each field being of fixed length. In general, thesame fields will be used for each message, although there may be somevariation. For example, a composite device may include an additionalinteger field including the number of sub-devices as explained below.

Preferably, the simple device description message is in the form of atoken-compressed message compressed from a human-readable messageformat, the message including a device type value representing the typeof the other device; the device type value being selected from a devicetype hierarchy having predetermined top level elements including acontroller device type and a basic device type, and at least one furtherlevel of subsidiary device types depending from the basic device typeand inheriting properties of higher level device types on which thesubsidiary device type depends, but not including any further level ofsubsidiary device types depending from the controller device type.

According to the preferred implementation of the HUCL protocol, theunderlying message format is a human readable format, such as XML.However, to save bandwidth, messages are passed between networkeddevices in compressed form. A networked device is nevertheless able toprocess such compressed messages, because the compression method used istoken compression, which replaces common strings with tokens. Thenetworked device can thus recognise the compressed tokens withoutdecompression, at least enough to recognise a query requiring a responseof a simple device description, and then respond with a simple devicedescription. Thus, a networked device can be implemented with littleoverhead.

A suitable form of token coding is described in “wap binary XML contentformat” of 24 Jun. 1999, available at the time of writing athttp://www.w3.org/TR/wbxml.

It will be noted that although there is preferably at least onehierarchy depending from a basic device type, i.e. a hierarchy ofcontrolled devices, there is no corresponding hierarchy of controllerdevices. This is to keep the simple device description messages as shortand simple as possible—many controllers, such as a universal remotecontrol, are capable of controlling a number of different device types.

Preferably, the plurality of networked devices include at least onesimple device without the capability to decompress messages andaccordingly which interprets directly compressed messages and at leastone complex device including a message decompression arrangement fordecompressing the messages and a message interpreter for interpretingthe decompressed messages.

In another aspect, the invention relates to an individual networkeddevice capable of responding to both simple and extended devicedescription query message.

Accordingly, in a second aspect, there is provided a networked deviceincluding:

-   -   a transceiver for sending and receiving messages: and    -   a message handler arranged to carry out the steps of:    -   on receiving a simple device description query message from one        of the other devices, sending to the other device a simple        device description message of defined length including a device        type value representing the type of the networked device; and    -   on receiving (an extended device description query message from        another device sending to the other device an extended device        description of variable length.

As well as networked devices capable of responding to such device querymessages, the invention also relates to devices generating device querymessages and processing the results.

Accordingly, in a third aspect there is provided a networked device,including a transceiver for sending and receiving messages:

-   -   a message handler arranged to carry out the steps of:    -   establishing the address of at least one other device;    -   sending a simple device description query message to another        device requesting a simple device description;    -   receiving from the other device a simple device description        message of fixed length including a device type value        representing the type of the other device and a field indicating        whether an extended device description is available;    -   and further arranged to optionally carry out the steps of:    -   testing the simple device description message to determine        whether an extended device description is available;    -   sending an extended device description query message to the        other device requesting an extended device description from the        other device; and    -   receiving from the other device an extended device description        of variable length.

The invention also relates to the methods of operation of the devices ofthe second and third aspects.

Accordingly, in a fourth aspect, the invention relates to a method ofoperation of a networked device, including: sending a simple devicedescription query message to one of the other devices requesting asimple device description; receiving from the other device a simpledevice description message of defined length including a device typevalue representing the type of the other device and a field indicatingwhether an extended device description is available; testing the simpledevice description message to determine whether an extended devicedescription is available, and if so sending an extended devicedescription query message to the other device requesting an extendeddevice description from the other device; and receiving from the otherdevice an extended device description of variable length.

In a fifth aspect, the invention relates to a method of operation of anetworked device, including:

-   -   receiving a simple device description query message from one of        the other devices requesting a simple device description;    -   sending to the other device a simple device description message        of defined length including a device type value representing the        type of the networked device;    -   receiving an extended device description query message from the        other device requesting an extended device description from the        networked device; and    -   sending to the other device an extended device description of        variable length.

As previously mentioned, the device type value may be selected from adevice type hierarchy having predetermined top level elements includinga controller device type and a basic device type, and at least onefurther level of subsidiary device types depending from the basic devicetype and inheriting properties of higher level device types on which thesubsidiary device type depends, but not including any further level ofsubsidiary device types depending from the controller device type.

A controller device according to the invention preferably includes acontrol input, and controls other devices based on signals received onthe control input. Further, the controller device may implement one ormore ways of determining what devices the controller can control.

One approach to deal with the lack of information when a device is acontroller device type is for the controller device to have thefunctionality to respond to an incoming controller query messagequerying whether the controller can control a predetermined device typeby responding with the lowest level of device type in the list of devicetypes that can be controlled by the networked device that either is thepredetermined device type or is a higher level device type from whichthe predetermined device type depends. The controller device can thensend control signals selected from a predetermined list of controlsignals to other devices in accordance with signals received on thecontrol input.

Instead of being a controller device, the device may be a controlleddevice having a device type of the basic device type or a device typedepending from the basic device type; the networked device having thecapability of responding to basic device instructions sent by acontroller, the instructions including at least a predetermined base setof instructions.

In order to cope with multifunctional devices, the predetermined toplevel elements may include a composite device type with thefunctionality of a predetermined number of other device types, andarranged to respond to an incoming device query message requiring asimple device description by sending a simple device descriptionincluding the device type as a composite device and the instantaneousnumber of other device types.

The networked device may include a memory storing a predetermined simpledevice description message, wherein the description message is a messagepre-compressed from a message in human readable form including a devicetype; a flag indicating if the sending device has an extended devicedescription available; and a predetermined number of additional flagsidentifying a predetermined number of additional status settings. Thus,rather than generating a simple device description message internally, asuitable message is pre-stored and sent out when required.

The invention also relates to a computer program for controlling anetworked device.

The system may include a number of simple devices, with simplefunctionality and no capability to decompress messages, and more complexdevices that decompress messages to interpret them and operate on them.The more complex devices can have much more complex functionality, atthe expense of increased overhead and processor power requirement.

In another aspect, the invention relates to a network establishment andmanagement protocol for controlling electronic devices, the protocolbeing recorded on a record medium, the protocol comprising: acompression algorithm defining the mechanism for compression of saidmessages; a definition of a generic message format, the messages beingXML compliant messages; and a definition of message sequencingrequirements.

The protocol may define controller devices and discovery for controllerdevices may be defined to include a mechanism for discovering acontrolling device and instructing said controlling device on its futureoperation.

The protocol may further define device description messages to be one ofa first message of fixed length and content, and a second message ofundefined length and content.

The protocol may define discovery of device description messages toallow piecemeal discovery of the second device description message.

The protocol may define composite devices and the device descriptionmessages of composite devices are defined to include the number ofsub-devices in the composite.

Discovery of device description messages of composite devices may bedefined to allow discovery of the sub-devices in turn.

For a better understanding of the invention, embodiments will now bedescribed purely by way of example, with reference to the accompanyingdrawings in which:

FIG. 1 shows a pair of devices communicating using an embodimentaccording to the invention;

FIG. 2 shows a schematic of the software in one device;

FIG. 3 is a flow diagram of the device discovery process;

FIG. 4 is a schematic of the device type hierarchy;

FIG. 5 shows the steps that a controller carries out to inform acontrolled device of its control capability of that device;

FIG. 6 shows the steps that a controller carriers out to determine itscontrol capability of a controlled device;

FIG. 7 is a flow diagram of the device discovery process for a compositedevice;

FIG. 8 illustrates an embodiment of a composite device;

FIG. 9 illustrates another embodiment of a composite device;

FIG. 10 shows the structure of the software;

FIG. 11 illustrates the HUCL protocol; and

FIG. 12 illustrates a simple device description message.

The protocol HUCL is a lightweight, low bandwidth control protocolprimarily designed for wireless systems. The messaging format is basedon XML, and messages are compressed prior to transmission. The use ofXML provides an extensible and scalable solution with the compressionreducing the data sent, so reducing the amount of time the transmitteris on and consuming power.

The general principles of the HUCL protocol and how it would operate ona device will now be discussed with reference to a simple example.

Referring to FIG. 1, a light switch 2 and a light fitting 4 areprovided. The light switch 2 has a physical rocker switch 6 operated bythe user, together with an RF transceiver 8 and battery 10, togetherwith control circuitry 12 and memory 14. The light fitting also has anRF transceiver 8 and memory 14, but is mains powered and has the controlcircuitry 20 to apply power to the light bulb 22. The light switch 2 isthus an example of a controller which has a control input 6 (theswitch), whereas the light fitting is an example of a controlled device4. The memory 14 in the controller includes a list 24 of device typesthat the controller can control, and control functions appertaining tothe device types. The memory 14 in both controlled 4 and controller 2devices also contains code 26 for causing the control circuitry to carryout the methods that will be described in more detail below.

FIG. 2 shows a representation of the software that resides on each ofthe devices in memory 14. The control application 30 communicates withthe HUCL Software Stack 32 when certain events occur.

In a similar way the HUCL Software Stack 32 communicates with the RFSoftware Stack 34, and the RF Software Stack 34 will communicate back tothe HUCL Software Stack 32 when certain events occur e.g. on receipt ofdata.

Messages 36 are sent and received. The messages may be of a number oftypes, including a simple device description query message, or any of anumber of other message types.

The operation of the devices will now be described with reference toFIG. 3. The first phase in the operation of this pair of devices is forthe switch to discover the address of the fitting. This is known asdevice discovery, and it is a requirement of the underlying RF transportstack that device discovery is either provided (in the RF SoftwareStack), or that it is possible to implement device discovery on top ofthe transport stack (in the lower layer of the HUCL Software Stack).

The discovery process is initiated 100 by the Control Application(possibly as a result of some user interaction) by performing a callinto the HUCL Software Stack requesting firstly the number of knowndevices, and then the network addresses of those devices. These deviceaddresses are returned.

Depending on the underlying RF protocol, the network addresses may beestablished in some other way.

The end result of the device discovery phase is that the ControlApplication is supplied 102 with a list of addresses of all devicesknown by the RF Stack. At this point in the process the ControlApplication knows nothing more about each other device other than itsaddress.

The second phase in the pairing process is for the Control Applicationto gather information on the devices for which it has addresses. Thisinformation is called the device description. The control applicationdoes this by making a call into the HUCL Software Stack, passing theaddress of the device that it requires the device description from.

The request for the simple device description is then passed 104 overthe RF link to the destination device, so in the switch/fitting exampledescribed above the request is transmitted from the switch to thefitting. On receiving the request, the HUCL Software Stack at thedestination device makes a call in to the Control Application requestingthe device description. The format of the description is defined. If notalready in a compressed form the description is compressed before beingtransmitted back to the sender of the request.

When the HUCL Software Stack on the requesting device receives 106 thedevice description, it is passed up to the Control Application. At thispoint the application has some basic information about the device andcan make the decision as to whether it wished to communicate furtherwith this device.

A design goal of HUCL is that it is suitable to operate on very simpledevices, however the information necessary to fully describing a deviceis potentially quite complex. The list below shows the sort ofinformation a device might want to provide as part of its description.

-   -   Device Type e.g. DVD    -   Vendor Name e.g. Philips    -   Model Number e.g. DVD1010/002    -   Serial Number e.g. AH06848032345    -   Vendor URL e.g. www.philips.com

For the simplest of control devices, such as the switch used in theexample throughout this section, much of this information is probablyredundant. It would however be of use on a higher end ‘PDA’ type remotecontrol that has a screen where such information could be displayed tothe user.

The processing of such descriptions on low-end devices can present aproblem, since it would potentially need the storage (RAM) to cache thecomplete message as it was received. The problem is worse than it mightat first seem, since the overall size of the description data shownabove is indeterminate, much of the information is ‘free text’; thevendor name could be very long, the URL could specify an exact pagemaybe even with parameters e.g.http://www.consumer.philips.com/global/b2c/ce/catalog/subcategory.jhtml?groupld=VIDEO&divld=0&catld=DVD&subCatld=DVDPLAYER

The way in which this is overcome in HUCL is that the device descriptionis split into two tiers of information. The first tier is a simplisticdescription of the device but identifying if further information isavailable. It does not contain any free text fields so the overalllength of it is deterministic. The second tier of extended informationis optional but provides additional information.

Referring to FIG. 12, the Simple Device Description message 230 includesas fields the device type 232, a field 238 to indicate if ExtendedDevice Description available and other fields 236 identifying keyinformation e.g. a flag to indicate if event subscription is available.Optional integer field 234 represents the number of sub-devices of acomposite device. The skilled person will appreciate that the message230 may also include a header and footer which are omitted forsimplicity. The message will include compressed XML tokens which arelikewise omitted for clarity. The fields of the Simple DeviceDescription are all of fixed length, so that they can be dealt withreadily without decompression.

After receiving 106 (FIG. 3) the Simple Device Description 230 theSimple Device Description 230 is passed back to the HUCL Stack.

If the Extended Device Description is available and the controllerdevice requires it, the controller device Control Application may issuea “GetExtendedDescription” request 108 back to the device.

The HUCL Stack on the device receiving this request makes a Get ExtendedDescription call into the Control Application requesting the ExtendedDevice Description.

The Extended Device Description is passed back to the HUCL Stack, andmakes its way back to the Control Application on the device thatrequested it. The Extended Description is then returned 110 to therequesting device.

If a GetExtendedDescription query is received on a device that does notprovide an Extended Device Description the request is simply ignored.

Returning again to the switch/fitting example used throughout thissection, from the point when the switch knows only the address of thefitting, the switch requests from the fitting its Simple DeviceDescription. On receiving this it provides sufficient information suchthat the switch knows that it is talking to a light fitting thatconforms to the standard fitting command set, it also knows that (forexample) the fitting can't provide any Extended Device Description.

It is mandatory for a device application to provide a Simple DeviceDescription to the HUCL Stack when requested. A device that does notprovide any Extended Device Description can ignore any requests itreceives for such information.

Included in the Simple Device Description returned by a device (whenrequested) is the device type field 232 that identifies the type of thedevice, e.g. TV, DVD, Light Fitting etc. The Device Type field 232 willidentify to the controller (requesting the Simple Device Description)the instruction set that the device conforms to. HUCL devices identifythemselves simply by their type identifier, they do not then go on tosend messages to describe how they are controlled; there is no ‘runtime’service description concept in HUCL. If a device identifies itself as alight fitting then the command set that can be called on this device isidentified in the HUCL specification for a Light Fitting type device.

Referring to FIG. 4, all device types depend from a base device type 50.Top level elements 58 include in this example the controller device type52, a basic device type 54 for controlled devices and an alarm devicetype 56.

Subsidiary device types 68 depend from the basic device type. In theexample, these include a TV device type 64, a dimmable light device type62 and a PVR device 60.

The Device Type Classification was to produce a system aims to allow asimple controller to identify whether it could control a device to theextent of the controllers' capabilities.

A simple switch could be paired with a light fitting to turn on and offa light, but one might argue that the control functionality of theswitch, that is its ability to turn a device on or off should beapplicable to any device than can accept an on/off concept e.g. a TV,Heater, Printer.

One way in which this could be implemented is for the switch to have alist of all of the devices it knows how to control (turn On or Off), sowhen it requests the Simple Device Description for a device, it can lookat the Device Type field in the returned description and determine if itis within its list of device types it knows how to control.

There are two significant drawbacks of this approach. Firstly the switchis a very simple device and it is undesirable for the application withinit to have to hold a list of all possible devices that it could control,which would be quite large; secondly if a new type of device is createdafter the switch is produced (which can accept simple On Offfunctionality), then the switch will not have this new device type inits list, and will not believe it can control it i.e. it is notextensible.

HUCL classifies devices in a hierarchical way, shown in FIG. 4. TheDevice Type field 232 (FIG. 15) identifies the device within thehierarchy and so even if new devices were created, as long as it isderived from an the appropriate point within the hierarchy, a simpleswitch would still know that it could control it to an extent.

Devices that fall lower in the tree inherit the functionality of devicetypes above it. It may be necessary to add some interpretation to thecommands when applied to lower devices in the tree, for example theOn/Off command when sent to a light will fairly obviously turn it On andOff, but the same commands when sent to a TV would place it in and outof standby mode.

The key benefit of the Device Type hierarchy is that even if thecontroller has no knowledge of the specific device type itself, it candetermine the device from which it is derived, of which it may have someknowledge and hence may be able to control the device to some lesserextent (from the perspective of the device).

For example, consider the case that a light switch obtains the addressof a device, it requests from this device the Simple Device Description;the Device Type field identifies the device as TV, but the switch doesnot recognise this as a device it knows about. However the switch canalso establish from the description that it is a derivative of the‘Basic Device’, which it does know about. The net result is that theswitch can control the TV, to the extent of the controllers capabilitiesi.e. On and Off, despite knowing nothing about the device itself. Thedevice could be a brand new category of device called an ‘XYZ’ inventedlong after the switch was manufactured, but so long as it is derivedfrom a Basic Device the switch can still control it to an extent.

Although the Device Type Hierarchy may have just two tiers, andcontroller and basic device top level elements, at least one furthertier and/or top level element is desirable. This caters for devices thatwould not comply with the functionality shown above in the Basic Devicethat is devices that do not have basic ‘Turn On’ ‘Turn Off’functionality, e.g. an alarm. For illustrative purposes an ‘Alarm’ typedevice 56 has been shown in FIG. 4 and understandably this ‘Alarm’device does not want to implement the normal On/Off functions thatdevices that are derived from Basic Device must have; it therefore sitsat the same top level 58 in the hierarchy as the Basic Device 54 itself.

A second extension to the hierarchy is also shown in FIG. 4 i.e. theEnhanced TV Device 66 below the normal TV Device 64. Here the EnhancedTV Device inherits all of the functionality of both the Basic Device 54and the TV Device 64, but also includes some extended functionality thatis not present in a normal TV. A regular TV remote control designed tooperate a normal TV Device can operate the Enhanced TV Device to thelevel of a normal TV Device functionality, but can't control theextended functionality.

The HUCL protocol accordingly provides an extensible mechanism fordescribing the Device Type and the devices above it from which itinherits functionality. Whilst the idea of a hierarchy of many layersmight seem appealing, extending it beyond three or four levels willstart to impact the size of the Simple Device Description.

Within HUCL it is possible to request a device description from acontroller as well as a controllable device. When one device sends the“Get Simple Description” to a controller device (e.g. a switch) it isreturned a Simple Device Description that contains a Device Type of“Controller”. The controller device may also make available an ExtendedDevice Description which provides further information such as themanufacturer, model number etc.

It is important to note that the Device Type returned by a controllerdevice is simply “Controller” 52 there is no hierarchy of differentcontroller type devices defined in the device type tree. The reason forthis is again trying to keep the protocol and messages sizes small andsimple. It might be felt that it would be possible to have differentcontroller types derived from the basic Controller such as a Switch, TVRemote Control, PVR Remote Control, etc. However a problem would occurwith intelligent controllers such as Universal Remote Controller thatare capable of controlling a wide range of devices. To include all ofthe possible controller types in a simple device description wouldresult in a potentially large message, which goes against the ideal oftrying to make the initial Simple Device Description simple. Todetermine the exact capabilities of a controller device differentmechanisms are employed.

The first means of determining the capabilities of a controller deviceis by the Extended Device Description which is permitted on a controllerdevice and may contain information such as the device name e.g.“Universal Remote Control” and whilst this is textual information and isnot directly interpretable by application software, it can be presentedto the user to assist in making an informed choice about a controller.

The second means for a device to determine more about a controller is byquerying it.

The use of querying is a powerful mechanism for drip-feeding informationabout a device that would otherwise, if supplied en-mass, overload therequester.

Each device of controller type provides a means for other devices toquery 120 whether it is able to control a specific Device Type (FIG. 5).The device type passed in the query is the same field as is used in theSimple Device Description i.e. as defined in the Device Type Hierarchy.The controller returns 122 the level to which it can control the device,by returning the lowest device type in a list stored in the controllermemory 14 that is the device type passed in the query or from which thatdevice type depends. For example, a simple switch is queried whether itcan control an Enhanced TV Device. Based on the hierarchy illustrated inFIG. 4 above the reply is that it can control it to the level of BasicDevice. The switch would typically itself know nothing about a devicetype of Enhanced TV Device, but since the Device Type also includes theinherited devices it would be able to identify the Basic Device andreturn this as the lowest hierarchically superior device type it iscapable of controlling.

The controller also implements an algorithm to determine if the switchcan control a device type that is returned to it in a Simple DeviceDescription (FIG. 6). When a switch discovers the address of a device itasks 124 the device for its simple device description, on receiving thisinformation 126 the switch tests 128 whether it can control a device ofthis type to any degree, which is the same question it needs to respondto as a result of the querying process 120. The result is that the twoquery processes 120, 122, 124, 126, 128 do not add too much to thecomplexity of the simple switch device. The same applies to other simpledevices.

It can be foreseen that there will be instances where a device may be acomposition of a number of discrete devices all accessed via the samephysical address e.g. all co-located on a single RF transceiver.

Examples of this type of device are a bank of individually switchablelights controlled through a single RF transceiver, or a TV withintegrated alarm clock where both components are remotely controllableagain through the same transceiver.

FIG. 7 illustrates the discovery process. The switch initially obtainsthe addresses of all devices known by the underlying transport medium,this includes the single address of the four individually controllablelights. The switch issues 140 a Get Simple Description command to thelight bank, and the question that arises is what should the reply be? Iffour device descriptions are returned then this would be four times asmuch data than the switch would be expecting to receive. Returningmultiple Simple Device Descriptions is not very scalable, and would, forexample cause problems if there were 20 lights in the lighting bank.

The solution for this provided by HUCL is a specific Device Type forcomposite devices.

The composite device returns 142 its Simple Device Description includingin the Device Type field 232 its device type as a “Composite Device”.The Simple Device Description also identifies in field 234 that thereare, in this example, four embedded devices within this single device.

The next stage, once the controller has identified that it iscommunicating with a composite device, is for it to establish whatdevices are embedded within it. The controller makes 144 further GetSimple Description requests to the composite device but addressing therequests to the specific embedded devices. The embedded devices return146 their device descriptions.

Once the controller decides that it is going to control one of theembedded devices, all control commands are directed at the specificembedded device by including an embedded device ID with each command.Once the concept of the composite device has been established it opensup the possibility for a number of interesting device combinations thatwould be of benefit, some of these will be discussed below.

An example is a single device that consists of a lamp with integralswitch, where the functionality of switch is exposed so as to be able tocontrol other devices. This device, when queried for its Simple DeviceDescription exhibits itself as a composite device, but when queriedfurther one embedded device would be found to be a controller, and theother a controllable i.e. a Light Device. A number of such devices couldbe configured in such a way that operating the switch on any one of thedevices causes the lights to be turned On/Off on all the devices e.g.turning on any one table lamp in the lounge causes all the table lampsin the lounge to come on.

Other possible combinations of composite device within the CE domaininclude for example a TV+video cassette recorder (VCR) or DVD and VCR.Each of these could if required describe itself as a composite of twodevices.

Conceptually a Device consists of the core device plus zero or moresub-components, e.g. a TV Device 60 may for example consist of the TVDevice 60 itself plus Tuner 64, Audio 66 and Display 68 sub-components(see FIG. 8).

It is also conceivable that a single device may have more than oneinstance of a sub-component e.g. a TV/VCR Combi Device may have twotuners 62, 64, one for the TV and one for the VCR (see FIG. 9), as wellas audio 66 and display 68 components.

It might be felt that the use of XML and its compression andde-compression on the simplest of devices is a little heavyweight. Theuse of XML to describe the protocol provides a solution that is easilyextensible for future enhancements, relatively simple to describe andunderstand, can easily handle structured information and is instantlycompatible with the ‘internet domain’.

Using a tagged compression technique on the XML (defined within HUCL)takes the relatively verbose protocol back down in size towards that ofa traditional pure binary-based protocol, with some additional overheadto retain the content structure.

If one were to be presented with the a command in its compressed form itcan be read in a similar manner that one would read any other binarybased protocol, using information on the command structure and a tableof definitions for data values. The only hint that the binary data mayhave originated from an XML based notation would be the presence of datato represent structure.

The HUCL specification defines that the messages is always transmittedthrough the transport medium in its compressed form. However on a simpledevice the application may operate directly on compressed messages, soeliminating the need on that device for the presence of thecompression/de-compression software within the HUCL Software Stack. Inthis case the application would store (as part of the application imagein ROM) the simple device description in its pre-compressed form, itwould have a parser for the compressed protocol messages that itreceives which would be similar in nature to any other binary protocolparser; any response messages would also need to be stored in theircompressed form.

Using this approach the simplest devices such as the light switch andlight fitting example used throughout this section can be implementedwith a reduced software stack, and given that the number of commandsthat a simple device would need to understand and send is relativelysmall (turn light on, turn light off, toggle, get current state, getdevice description etc.) the overhead on the application software isminimal.

This offers a scalable solution to devices, where it is practical toimplement the application to operate on compressed data this can bedone, but when the device becomes more complex there will be a pointwhere it becomes easier to include the compression/de-compressionfunctionality in the stack and have the application use the protocolmessages in their full XML notation. This cut off point is entirely downto the device designer and not defined or dictated by HUCL at all.

FIG. 10 illustrates how the components that make up HUCL fit together.It will be appreciated that the components are software componentsrecorded in memory.

The following sections discuss in more detail the layers that form theHUCL software stack 32 and the functionality that they provide.

As has been stated earlier HUCL does not rely on a specific transportprotocol (unlike for example TCP/IP) but instead sits directly on top ofa transport stack 34. Different transport stacks 34 will by their natureoffer differing services to applications and through differing API's;the HUCL Transport Adaption Layer 180 acts as a buffer to the specifictransport layer.

The Transport Adaption Layer 180 provides to the higher layers in theHUCL stack a consistent transport independent set of services. Therequirements of this layer are defined in detail in the ProtocolSpecification.

The messaging layer 182 provides the bulk of the functionality of theHUCL Software Stack. Applications communicate with this layer throughthe HUCL API and it will perform the calls back in to the applicationwhen necessary (e.g. when data is received).

The messaging layer 182 also handles any initial error reporting and ifnecessary acknowledgements. Message ID's and Transaction ID's used tocheck for missing messages and for coupling messages to replies are alsohandled fully by this layer.

The Messaging layer 182 also makes use of the Compression/Decompressionservices 184 as and when a message needs to be compressed ordecompressed. As discussed earlier an application deals exclusively withmessages in their compressed form, no calls are made to these servicesand they can be removed from the runtime stack.

Quite simply the compression and decompression services provide themessage layer with the means to convert the HUCL messages between theircompressed and decompressed forms. It is possible for this component ofthe system to be absent in low-end devices where all data exchanges withthe application are made with compressed messages.

The application programming interface API 186 is the interface throughwhich all applications communicate with the HUCL software Stack.Communication is bi-directional in that the HUCL stack will makeasynchronous calls back to the application as a result of certain eventsoccurring in the lower layers e.g. message received via the transportstack.

HUCL is transport stack 34 independent, and what this means is that theHUCL messaging protocol can be built on top of a variety of transportstacks, both wired and wireless.

Since HUCL is designed as a lightweight protocol it is therefore mostsuited to lightweight transport stacks as well such as the emergingZigbee (802.15.4) standard, but it can sit equally well on top of TCP &UDP/IP which opens up a wide range of other protocols, both wired (e.g.Ethernet) and wireless (e.g. 802.11b).

For a HUCL to be implemented on a transport stack 34 it must be possibleto provide a number of services to the messaging layer of the HUCLstack. This means that these services can either be present in thetransport stack itself or it must be possible to implement any missingservices in the Transport Abstraction Layer of the HUCL stack. Theseservices may cover aspects such as addressing, message delivery anddevice discovery (e.g. discovering the addresses of other devices on thenetwork).

The protocol itself is a document recorded on a medium 214, includingthe following information as shown in FIG. 11:

-   -   a generic HUCL message format 200 that defines the format to        which all HUCL messages conform;    -   message definitions 202 defining the specific messages that form        the control protocol.    -   message sequencing requirements 204 defining which messages are        sent when, and the requirements of the application on receiving        a message.    -   the HUCL API definition 206 defining the bi directional        interface between HUCL and the application using it;    -   the messaging System requirements and functionality 208 of the        HUCL software stack;    -   a compression algorithm 210 defining the mechanism for the        compression of the HUCL messages, and    -   a transport Adaption Layer definition 212 defining how the HUCL        software stack is interfaced to a transport system (e.g. an RF        stack).

HUCL is accordingly not simply a message format definition but alsoencapsulates a message interchange and compression. The later four itemsin the list above form the HUCL software stack that would be present ina device, the first three items define the requirements to which thestack and application must conform.

From reading the present disclosure, other variations and modificationswill be apparent to persons skilled in the art. Such variations andmodifications may involve equivalent and other features which arealready known in the design, manufacture and use of networks and whichmay be used in addition to or instead of features described herein.Although claims have been formulated in this application to particularcombinations of features, it should be understood that the scope ofdisclosure also includes any novel feature or any novel combination offeatures disclosed herein either explicitly or implicitly or anygeneralisation thereof, whether or not it mitigates any or all of thesame technical problems as does the present invention. The applicantshereby give notice that new claims may be formulated to any suchfeatures and/or combinations of such features during the prosecution ofthe present application or of any further applications derivedtherefrom.

In particular, the specific subroutine names used in the examples mayreadily be varied. The computer program controlling the devices is shownas being recorded in memory 14 but the skilled person will realise thatit could be recorded on many other types of record carrier such as a CD,floppy disc, etc.

Further, it will be noted that a very simple example of a light fittingand light switch has been extensively described in the forgoing. Theskilled person will appreciate that many more complex control scenariosare also possible.

1. A method of operation of a networked device in a network having atleast one other device, the method including: sending (104) a simpledevice description query message to at least one other device requestinga simple device description; receiving (106) from the other device asimple device description message of defined length including a devicetype value representing the type of the other device; sending (108) anextended device description query message to the other device requestingan extended device description from the other device; and receiving(110) from the other device an extended device description of variablelength.
 2. A method according to claim 1 further including establishing(102) the network address of another device or other devices before thestep of sending (104) a simple device description to at least one otherdevice.
 3. A method according to claim 1 or 2 wherein the simple devicedescription message (230) is in the form of a token-compressed messagecompressed from a human-readable message format, the message including adevice type value (232) representing the type of the other device; thedevice type value being selected from a device type hierarchy havingpredetermined top level elements including a controller device type (52)and a basic device type (54), and at least one further level ofsubsidiary device types depending from the basic device type andinheriting properties of higher level device types on which thesubsidiary device type depends, but not including any further level ofsubsidiary device types depending from the controller device type.
 4. Amethod according to claim 3 wherein the networked device is a controllerdevice (2) comprising a list (24) of device types that the controllercan control.
 5. A method according to claim 4, the method furtherincluding determining whether the networked device can control anotherdevice by: determining the lowest level of device type that either isthe device type of the other device or is a higher level device typefrom which the device type of the other device depends, in the list ofdevice types that can be controlled by the controller, to determine theextent to which the networked device can control the other device.
 6. Amethod according to claim 5 further including: receiving a controllerquery message from another device including an requested device typevalue to request whether the controller is able to control a device ofthe requested device type; and responding with a controller responsemessage including a device type value representing the lowest level ofdevice type in the list of device types that either is the requesteddevice type or is a higher level device type from which the requesteddevice type depends.
 7. A method according to claim 2 wherein thepredetermined top level elements in the device type hierarchy furtherinclude a composite device type, and the networked device is of thecomposite device type having the functionality of an integer number ofother devices, the method further comprising: responding to a receivedsimple device description query message by sending a simple devicedescription message (230) including the device type value (232)representing the device as a composite device and further an integersub-device number being the number (234) of other devices.
 8. A methodof operation of a networked device, including: receiving (104) a simpledevice description query message from one of the other devicesrequesting a simple device description; sending (106) to the otherdevice a simple device description message of defined length including adevice type value representing the type of the networked device;receiving (108) an extended device description query message from theother device requesting an extended device description from thenetworked device; and sending (110) to the other device an extendeddevice description of variable length.
 9. A networked device, including:a transceiver (8) for sending and receiving messages: and a messagehandler (26, 182) arranged to carry out the steps of: on receiving (104)a simple device description query message from one of the other devices,sending (106) to the other device a simple device description message ofdefined length including a device type value representing the type ofthe networked device; and on receiving (108) an extended devicedescription query message from another device sending (110) to the otherdevice an extended device description of variable length.
 10. Anetworked device according to claim 9 wherein the simple devicedescription message (230) is in the form of a token-compressed messagecompressed from a human-readable message format, the message including adevice type value (232) representing the type of the other device; thedevice type value being selected from a device type hierarchy havingpredetermined top level elements including a controller device type (52)and a basic device type (54), and at least one further level ofsubsidiary device types depending from the basic device type andinheriting properties of higher level device types on which thesubsidiary device type depends, but not including any further level ofsubsidiary device types depending from the controller device type.
 11. Anetworked device, including: a transceiver (8) for sending and receivingmessages: a message handler (26, 182) arranged to carry out the stepsof: sending a simple device description query message to another devicerequesting a simple device description; receiving from the other devicea simple device description message of fixed length including a devicetype value representing the type of the other device and a fieldindicating whether an extended device description is available; andfurther arranged to optionally carry out the steps of: testing thesimple device description message to determine whether an extendeddevice description is available; sending an extended device descriptionquery message to the other device requesting an extended devicedescription from the other device; and receiving from the other devicean extended device description of variable length.
 12. A networkeddevice according to claim 11 wherein the simple device descriptionmessage (230) is in the form of a token-compressed message compressedfrom a human-readable message format, the message including a devicetype value (232) representing the type of the other device; the devicetype value being selected from a device type hierarchy havingpredetermined top level elements including a controller device type (52)and a basic device type (54), and at least one further level ofsubsidiary device types depending from the basic device type andinheriting properties of higher level device types on which thesubsidiary device type depends, but not including any further level ofsubsidiary device types depending from the controller device type.
 13. Anetworked device according to claim 12 wherein the networked device hasthe controller device type, wherein the networked device comprises alist of device types that can be controlled by the networked device, sothat the networked device can determine the extent to which thenetworked device can control another device by determining the lowestlevel of device type that either is the device type of the other deviceor is a higher level device type from which the device type of the otherdevice depends, in the list of device types that can be controlled bythe controller.
 14. A networked device according to claim 13 wherein themessage handler is arranged: to receive a controller query message fromanother device including an requested device type value to requestwhether the controller is able to control a device of the requesteddevice type; and to respond with a controller response message includinga device type value representing the lowest level of device type in thelist of device types that either is the requested device type or is ahigher level device type from which the requested device type depends.15. A system, comprising a plurality of networked devices each having atransceiver for sending and receiving network messages; at least onenetworked device arranged to send a simple device query message to otherdevices and to receive and interpret simple device description messagessubsequently received from the other devices; at least one networkeddevice arranged to send an extended device query message to otherdevices and to receive and interpret extended device descriptionmessages subsequently received from the other devices; each of thenetworked devices being arranged to respond to an incoming simple devicequery message from another of the devices by sending a simple devicedescription message of defined length including a device type valuerepresenting the type of the device; and at least one of the networkeddevices is arranged to respond to an incoming extended device querymessage from another of the devices by sending an extended devicedescription message.
 16. A system according to claim 15, wherein theplurality of networked devices include at least one simple devicewithout the capability to decompress messages and interpreting directlycompressed messages and at least one complex device including a messagedecompression arrangement (184) for decompressing the messages and amessage interpreter for interpreting the decompressed messages.
 17. Asystem according to claim 15 or 16 wherein the predetermined top levelelements further include a composite device type; the system includes atleast one networked device of the composite device type having thefunctionality of a predetermined number of other devices, thepredetermined number being an integer greater than or equal to 2; andeach of the at least one networked device of the composite device typeresponds to an incoming device query message requiring a simple devicedescription by sending a simple device description (230) including thedevice type (232) as a composite device and a sub-device number (234)representing the predetermined number of other devices.
 18. A computerprogram for controlling a networked device, the computer program beingarranged to cause the networked device to carry out the steps of amethod according to any of claims 1 to
 8. 19. A computer program forcontrolling a networked device, the networked device having a transportstack and an application, the computer program comprising: codeimplementing a transport adaption layer (180) for interfacing with thetransport stack; code implementing an application programming interface(186) for interfacing with the application; and code implementing amessaging layer (182) including the capabilities of sending andreceiving messages in a token-encoded human readable messaging format,the code being arranged to cause the networked device: to recogniseincoming device query messages requiring a simple device descriptionresponse and to provide a simple device description response including adevice type; and to recognise incoming device query messages requiringan extending device description and to respond with an extended devicedescription.
 20. A computer program according to claim 18 or 19 recordedon a data carrier (14).
 21. A network establishment and managementprotocol for controlling electronic devices, the protocol being recordedon a record medium, the protocol comprising: a compression algorithm(210) defining the mechanism for compression of said messages adefinition (200) of a generic message format, the messages beingcompressed XML compliant messages; and a definition (204) of messagesequencing requirements.
 22. A system in accordance with a networkestablishment and management protocol for combining electronic devicesaccording to claim 21.